Scopes & Mask Tabs disappeared from UV/Viewer screen
I figured it out.  I looked in space_image.py and found the following code.  

class ImageScopesPanel:
    @classmethod
    def poll(cls, context):
        sima = context.space_data
        if not (sima and sima.image):
            return False
        # scopes are not updated in paint modes, hide
        if sima.mode == 'PAINT':
            return False
        ob = context.active_object
        if ob and ob.mode in {'TEXTURE_PAINT', 'EDIT'}:
            return False
        return True

I could not quickly figure out the meaning of each of the variables, but decided to take a look at what could turn off the "scopes" tab.  As soon as I turned the "3D View" from "Edit Mode" to "Object Mode", the "Scopes" tab re-appeared on the "UV/Image Editor".